Q Condensation forms on the under ceiling of a screened-in back porch. In the fall I enclose the area with plastic frames, and the only heat is from the sun. During severe cold weather the ceiling becomes frosty, warms, and moisture drops to the floor. There is no roof leak. As long as snow is on the roof, I have this condensation problem. What's the solution?
Gladys Meyers Island Lake, Ill.
Insulate the ceiling between the rafters. If the rafters are now visible, install blanket insulation between the rafters in a thickness that is equal to their dimension. You may then want to cover the under part of the rafters with a finish material such as gypsum wallboard.
If the rafters are invisible because a ceiling exists on the under part of the rafters, get in touch with a reputable insulation contractor to blow thermal insulation between the rafters.
The cause of the condensation is the cold outside air contacting, through the sheathing, the somewhat warmer air within the porch. The insulation should provide a thermal barrier separating these two temperature differentials.
If a new porch roof is needed at this time, an alternate insulating method is to install rigid insulating board under the new roofing. The rigid board thickness should be sufficient to resist thermal transmission, but not so thick as to be architecturally unacceptable at the roof perimeter, where a cover edge board may be required.